To make onions: Cook bacon over medium-high heat in a large 12 inch skillet until crisp. Remove to paper towels to drain, reserve drippings in skillet.
Slice onions into ¼ inch rounds discarding the root and skin. Separate the rings and add to bacon drippings (or olive oil) in skillet. Add salt, pepper and red pepper flakes, mix well.
Cook onions uncovered over medium heat stirring occasionally for 10-15 minutes or until the onions are translucent and starting to soften.
Add the Coca-Cola to the skillet and stir to combine. Continue to cook over medium-low heat uncovered for an additional 20-30 minutes or until softened, caramelized and browned. Most of the liquid should be cooked out. Remove from heat and set aside.
To make burgers: Meanwhile, make the burgers. In a mixing bowl, use hands to mix together ground beef, bbq sauce, seasoned salt, pepper, granulated garlic and onion powder.
Divide the meat mixture into 6 even patties. Press centers to indent. (this helps prevent them from rising in the middle while cooking.) Place onto a sheet pan and chill until grilling.
To cook: Preheat grill to medium-high heat. Oil grates. Once hot, cook burgers for around 5-8 minutes on the first side, flip them over and continue to cook until your desired doneness or temperature is reached. Do not overcook. (165°F = well done) Top with a slice of cheese in the last few minutes of grilling, then remove to a platter.
Build burgers on toasted brioche buns with bacon, tomato slices, lettuce and dressed with your favorite condiments.
Top with caramelized Coca Cola onions and top bun then serve immediately.